The present invention relates to a photothermographic material. In particular, the present invention relates to a photothermographic material for scanners, image setters and so forth, which is particularly suitable for photographic art. More precisely, the present invention relates to a photothermographic material that shows high image density (Dmax) and low humidity dependency during development for developed character line width, in particular, little growth of line width during development under conditions of high temperature and high humidity.
There are known many photosensitive materials having a photosensitive layer on a support, with which image formation is attained by imagewise light exposure. Those materials include those utilizing a technique of forming images by heat development as systems that can contribute to the environmental protection and simplify image-forming means.
In recent years, reduction of amount of waste processing solutions is strongly desired in the field of photographic art from the standpoints of environmental protection and space savings. Therefore, development of techniques relating to photothermographic materials for photographic art is required, which materials enable efficient exposure by a laser scanner or laser image setter and formation of clear black images having high resolution and sharpness. Such photothermographic materials can provide users with simpler and non-polluting heat development processing systems that eliminate the use of solution-type processing chemicals.
Methods for forming images by heat development are described in, for example, U.S. Pat. Nos. 3,152,904 and 3,457,075 and D. Klosterboer, xe2x80x9cThermally Processed Silver Systems Axe2x80x9d, Imaging Processes and Materials, Neblette, 8th ed., compiled by J. Sturge, V. Walworth and A. Shepp, Chapter 9, p.279, (1989). Such photothermographic materials comprise a reducible non-photosensitive silver source (e.g., silver salt of an organic acid), a photocatalyst (e.g., silver halide) in a catalytically active amount and a reducing agent for silver, which are usually dispersed in an organic binder matrix. While the photosensitive materials are stable at an ordinary temperature, when they are heated to a high temperature (e.g., 80xc2x0 C. or higher) after light exposure, silver is produced through an oxidation-reduction reaction between the reducible silver source (which functions as an oxidizing agent) and the reducing agent. The oxidation-reduction reaction is accelerated by catalytic action of a latent image generated upon exposure. The silver produced from the reaction of the reducible silver salt in the exposed areas shows black color and provides contrast with respect to the non-exposed areas, and thus images are formed.
In many of conventionally known photothermographic materials, image-forming layers are formed by coating a coating solution using an organic solvent such as toluene, methyl ethyl ketone (MEK) and methanol as a solvent. However, not only use of an organic solvent as a solvent adversely affect human bodies during the production process, but also it is disadvantageous in view of cost because it requires process steps for recovery of the solvent and so forth.
Accordingly, methods of forming an image-forming layer by coating a coating solution using water as a solvent have been proposed. For example, Japanese Patent Laid-open Publication (Kokai, hereinafter referred to as JP-A) 49-52626, JP-A-53-116144 and so forth disclose image-forming layers utilizing gelatin as a binder, and JP-A-50-151138 discloses an image-forming layer utilizing polyvinyl alcohol as a binder. Furthermore, JP-A-60-61747 discloses an image-forming layer utilizing gelatin and polyvinyl alcohol in combination. As another example, JP-A-58-28737 discloses an image-forming layer utilizing a water-soluble polyvinyl acetal as a binder. If these binders are used, image-forming layers can be formed by using a coating solution comprising an aqueous solvent, and therefore considerable merits can be obtained with respect to environment and cost.
However, when a polymer such as gelatin, polyvinyl alcohol or water-soluble polyacetal is used as a binder, silver tone of developed areas becomes brown or yellow, which quite differs from black color regarded as a preferred proper color, and in addition, there arise, for example, problems that the blacking density in exposed areas becomes low and the density in unexposed areas becomes high. Thus, there can be obtained only images of which commercial value is seriously impaired. Furthermore, since such polymers show bad compatibility with the silver salt of an organic acid, there may also arise a problem that practically acceptable coatings cannot be obtained in view of coated surface quality.
European Patent Publication (hereinafter referred to as EP-A) 762,196, JP-A-9-90550 and so forth disclose that high-contrast photographic property can be obtained by incorporating Group VII or VIII metal ions or metal complex ions into photosensitive silver halide grains for use in photothermographic materials, or incorporating a hydrazine derivative into the photosensitive materials.
For use of photographic art films in the fields of newspaper printing, commercial printing and so forth, there have generally been desired systems that can provide stable images at any time. However, photothermographic materials showing such high-contrast photographic property as mentioned above, which is required for photographic art films, suffer from a problem that they show higher humidity dependency of character line width during development compared with conventional films to be treated with chemicals. In particular, line width is likely to increase during development under conditions of high temperature and high humidity.
Therefore, it has been desired to provide a photothermographic material that shows low humidity dependency of character line width during development and thus is suitable for use in photographic art.
Therefore, a first object to be achieved by the present invention is to provide a photothermographic material that shows high image density (Dmax) and low humidity dependency of character line width during development, in particular, as a photothermographic material for photographic art, more specifically, a photothermographic material for scanners, image setters and so forth.
A second object to be achieved by the present invention is to provide a photothermographic material that can be prepared by coating of an aqueous system, which is advantageous for the environment and cost.
The inventors of the present invention assiduously studied in order to achieve the aforementioned objects. As a result, they found that a photothermographic material that provides superior effects could be obtained by using a particular compound in a protective layer, and thus accomplished the present invention.
That is, the present invention provides a photothermogrpahic material having, on a support, an image-forming layer that contains at least a non-photosensitive silver salt of an organic acid, a photosensitive silver halide, a nucleating agent and a binder, and at least one protective layer outer than the image-forming layer on the support, wherein the protective layer contains at least one kind of compound represented by the following formula (1) as emulsion dispersion or solid dispersion.
Qxe2x80x94(Y)nxe2x80x94CZ1Z2Xxe2x80x83xe2x80x83Formula (1):
In the formula (1), Q represents an alkyl group, an aryl group or a heterocyclic group, which groups may have one or more substituents, Y represents a divalent bridging group, n represents 0 or 1, Z1 and Z2 represents a halogen atom, and X represents hydrogen atom or an electron-withdrawing group.
The present invention also provides a photothermographic material having, on a support, an image-forming layer that contains at least a non-photosensitive silver salt of an organic acid, a photosensitive silver halide, a nucleating agent and a binder, and at least one protective layer outer than the image-forming layer on the support, wherein a layer adjacent to the protective layer contains at least one kind of compound represented by the following general formula (2) as emulsion dispersion or solid dispersion. 
In the formula (2), M represents hydrogen atom or a k-valent cation, and k represents an integer of 1 or more. R represents a substituent and may form a salt when it can form a salt. n represents an integer of 1-4, and when n is 2-4, n of R may be identical or different from each other or one another.
It is preferred that the photothermographic material of the present invention has two or more protective layers outer than the image-forming layer on the support, and one of these layers adjacent to the image-forming layer contains at least one kind of compound represented by the formula (1) or (2) as emulsion dispersion or solid dispersion. Further, in the photothermographic material of the present invention, it is preferred that 50 weight % or more of total binder of the image-forming layer consists of polymer latex having a glass transition temperature of xe2x88x9230-40xc2x0 C., and 50 weight % or more of total binder of the protective layer consists of polymer latex having a glass transition temperature of 25-70xc2x0 C. The image-forming layer and the protective layer constituting the photothermographic material of the present invention are preferably formed by simultaneously coating them as stacked layers.
According to the present invention, there can be obtained photographic properties suitable for photographic art including little line width fluctuation and feasibility of securing sufficient image density (Dmax) even if heat development is performed in a high temperature and high humidity environment. Further, the present invention enables coating with an aqueous system, which is advantageous for environment and cost.
In the present specification, ranges indicated with xe2x80x9c-xe2x80x9d mean ranges including the numerical values before and after xe2x80x9c-xe2x80x9d as the minimum and maximum values.